Speaker
Description
Terahertz (THz) nonlinear optics is an emerging platform for studying strong-field light-matter interactions at low photon energies[1]. Because THz photon energies are far below typical interband transition energies, nonlinear responses are governed primarily by THz-driven thermodynamic response of the background Dirac carriers. In this regime, intraband acceleration of residual carriers and carrier heating play central roles[2]. These processes shape carrier transport and nonlinear optical response, motivating both fundamental studies and device concepts for nonlinear THz frequency conversion. High-harmonic generation (HHG) is a direct route to such conversion, producing phase-coherent spectral components at integer multiples of the pump frequency and upconverting THz signals into higher-frequency bands relevant to ultrahigh-speed information and wireless communications.
Graphene is a particularly attractive platform because its Dirac dispersion supports a strong intraband response and exceptionally large THz nonlinearities under ambient conditions3. Here, we use a table-top high-field THz platform with advanced THz spectral filtering to enable field-resolved characterization of nonlinear emission. Within this framework, we demonstrate enhanced third-harmonic generation (THG) by stacking graphene layers, applying electrostatic gating, and employing metasurface-assisted field engineering[3]. We then apply the same methodology to graphene oxide (GO), a chemically functionalized derivative of graphene, and observe THz HHG that includes phase-coherent spectral components at even harmonic positions. We investigate the origin of this signal by systematically ruling out incoherent, phase-random contributions and nonlinear responses from residual symmetry breaking. Overall, our results show that engineered graphene platforms can boost and tune THz nonlinearity, while GO can unlock non-perturbative pathways that broaden the accessible harmonic spectrum, supporting compact and reconfigurable THz components for frequency conversion and waveform engineering.
References
1. Hafez, H. A. et al. Adv. Opt. Mater. 8, (2020).
2. Hafez, H. A. et al. Nature 561, 507–511 (2018).
3. Maleki, A. et al. Light Sci. Appl. 14, 1–10 (2025).
| Keyword-1 | THz Nonlinear Optics |
|---|---|
| Keyword-2 | Graphene |
| Keyword-3 | High Harmonic Generation |